.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.com>
.\"
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.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
.\" Modified 2002-07-25 by Walter Harms
.\" 	(walter.harms@informatik.uni-oldenburg.de)
.\"
.TH ACOSH 3   2016-03-15 "" "Linux Programmer's Manual"
.SH NAME
acosh, acoshf, acoshl \- inverse hyperbolic cosine function
.SH SYNOPSIS
.nf
.B #include <math.h>
.sp
.BI "double acosh(double " x );
.br
.BI "float acoshf(float " x );
.br
.BI "long double acoshl(long double " x );
.sp
.fi
Link with \fI\-lm\fP.
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.ad l
.BR acosh ():
.RS 4
_ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
    || _XOPEN_SOURCE\ >=\ 500
.\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
    || /* Since glibc 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.RE
.br
.BR acoshf (),
.BR acoshl ():
.RS 4
_ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
    || /* Since glibc 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.RE
.ad b
.SH DESCRIPTION
These functions calculate the inverse hyperbolic cosine of
.IR x ;
that is the value whose hyperbolic cosine is
.IR x .
.SH RETURN VALUE
On success, these functions return the inverse hyperbolic cosine of
.IR x .

If
.I x
is a NaN, a NaN is returned.

If
.I x
is +1, +0 is returned.

If
.I x
is positive infinity, positive infinity is returned.

If
.I x
is less than 1,
a domain error occurs,
and the functions return a NaN.
.SH ERRORS
See
.BR math_error (7)
for information on how to determine whether an error has occurred
when calling these functions.
.PP
The following errors can occur:
.TP
Domain error: \fIx\fP is less than 1
.I errno
is set to
.BR EDOM .
An invalid floating-point exception
.RB ( FE_INVALID )
is raised.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbw28 lb lb
l l l.
Interface	Attribute	Value
T{
.BR acosh (),
.BR acoshf (),
.BR acoshl ()
T}	Thread safety	MT-Safe
.TE
.SH CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.

The variant returning
.I double
also conforms to
SVr4, 4.3BSD, C89.
.SH SEE ALSO
.BR asinh (3),
.BR atanh (3),
.BR cacosh (3),
.BR cosh (3),
.BR sinh (3),
.BR tanh (3)
